Found in central Florida new subdivision, I have never seen this. The pipe sticking up, is at all the homes. It is not a condensate line or H/W discharge.
Possibly vent, the kitchen is right there.
Any thoughts?
John I’m stumped but am looking forward to an answer.
Do you have a close up picture? Cannot see the top valve to well. Could be some type of pressure regulator.
Looks like a pressure relief valve.
under sink is AAV
in yard: backflow/airgap too avoid cross contamination, possibly irrigation related
In my last green build class we learned some places are recycling there grey kitchen water to water lawn and gardens. Could be vent for gray water tank?
Perhaps for the release of methane?
I knew the AVV, was not sure if it could be related to the kitchen sink as it is on the other side of the wall.
In the yard is an adjustable pressure relief valve. It could be for the irrigation system.
It has nothing to do with AAV under the sink.
Took a Full-Tine inspector to chime in. 
Full-Time-Professional Inspector
I do not believe it had anything to do with the sprinkler system as the reclaimed water was off and it was leaking from below the sod. The only thing it had in common with the kitchen sink was proximity.
This leaves us with pressure relief or back flow. I believe, given the direction of the arrows and being on the end of the plumbing line, it would be pressure relief.
Any other full time professional inspectors, Conspectors or part-time super inspectors have any good thoughts?
John - The sprinklers being “Off” do you mean not running or the water to the line was turned off?
The only thing I could find was here and it is an adjustable pressure relief valve.
http://www.fppi.com/products/list/159/adjustable-pressure-relief-valve.aspx
If the water line was still pressurized it could have still been leaking. To determine if it was to the house and leaking, just make sure all is off at the house and go to the meter and see if the meter is running.
All I could find…sorry if it does not help. thanks for asking, I am sure this will come up again. Let us know what you find out. Inquiring minds want to know.
All the water was off in the home and the meter was spinning. The house right next door had one also. They had zero lot lines and it was on the meter side. The sprinkler controller was about 15 ft away but the valves were on the opposite side of the house as was the reclaimed water.
Thanks for the help.
Possibly, but perhaps got the wrong anti-vacuum breakers valve installed:
At first I would have said it was for the irrigation but from the other information you are giving it seems to be for the water service.
It is for thermal expansion if the line pressure exceeds 90 psi it opens. 2007 code I think but you will find it in properties built earlier. Supposed to be under main shut off valve not where your picture shows it.
John I asked my plumbing contractor and here is his answer:
“It looks to be a expansion relief valve probably connected to the service line somewhere. And yes it does look to be. Adjustable”
Butch Ritter
Cape Coral Plumbing Inc.
5812 Enterprise Pkwy.
Fort Myers, FL. 33905
Pressure regulator and relief. John who built this one? Is the main water pipe under this and does it have a buried main shut off. I can’t believe the AHJ lets this crap go by that is just an accident waiting to happen. It is in a location that is subject to damage without protection. It is a clear code violation.